Lubricating oil compositions used to lubricate internal combustion engines contain a base oil of lubricating viscosity, or a mixture of such oils, and additives used to improve the performance characteristics of the oil. For example, additives are used, to improve detergency and dispersancy, to reduce engine wear, to provide stability against heat and oxidation, to reduce oil consumption, to inhibit corrosion, to act as a dispersant, and to reduce friction loss, among other attributes. However, each such additive is a separate component of the formulated lubricating oil and adds cost. Some additives provide multiple benefits, such as a dispersant/viscosity modifier. Other additives, while improving one characteristic of the lubricating oil, have an adverse effect on other characteristics. Thus, to provide a lubricating oil having optimal overall performance, it is necessary to characterize and understand all the effects of the various additives available, and carefully balance the additive content of the lubricant. Moreover, each of the additives is a separate component of the formulated lubricating oil and adds cost. Thus, it would be beneficial to have a single multi-functional additive that controls more than one performance characteristic of the lubricating oil without having an adverse effect on other properties of the lubricating oil.
For example, U.S. Pat. No. 4,234,435, discloses carboxylic acid acylating agents derived from polyalkenes and a dibasic carboxylic reactant such as maleic or fumaric acid or certain derivatives thereof. The acylating agents can be reacted with a further reactant such as polyethylene polyamines and polyols, to produce derivatives useful as lubricant additives.
U.S. Pat. No. 5,614,480, discloses lubricating compositions and concentrates which include carboxylic derivatives produced by reacting certain amines with a substituted succinic acylating agent containing at least about 50 carbon atoms in the substituent.
U.S. Pat. No. 6,107,258, discloses functionalized olefin copolymers that provide dispersancy properties, comprising acylated olefin copolymers containing a reactive carboxylic functionality reacted with a coupling compound which contains more than one amine, thiol and/or hydroxyl functionality which is also reacted with a performance enhancing compound which contains only one functional group capable of reacting with the carboxylic functionality of the acylated olefin copolymer.
Goldblatt et al., U.S. Pat. No. 6,410,652, issued Jun. 25, 2002, discloses a graft copolymer which is useful as a dispersant viscosity index improver and a method for making the graft copolymer. The disclosed method comprises the steps of (a) providing a graftable polymer or copolymer having a weight average molecule weight of from about 20,000 to about 500,000, an ethylenically unsaturated sulfur-, nitrogen- and/or oxygen-containing graftable monomer, and an amount of an initiator that is sufficient to graft such monomer and graftable copolymer or polymer; (b) introducing the aforesaid graftable copolymer or polymer into a melt-blending apparatus; (c) introducing the aforesaid graftable monomer into the melt-blending apparatus, (d) introducing the aforesaid initiator into the melt-blending apparatus, wherein at least one of the aforesaid graftable copolymer or polymer, graftable monomer and initiator is introduced into the melt-blending apparatus in the presence of at least either a polar or non-polar solvent; and (e) reacting the aforesaid graftable copolymer or polymer, monomer and initiator in the melt-blending apparatus, thereby forming the aforesaid graft copolymer as the product. The aforesaid Goldblatt et al. '652 also discloses a lubricating oil composition comprising a base oil and an aforesaid graft copolymer.
Goldblatt et al., U.S. Pat. No. 7,371,713, issued on May 13, 2008, discloses graftable monomers that are formed as the product of the reaction between an amine and an acylating agent. The reaction product is a graftable ethylenically unsaturated, aliphatic or aromatic monomer having nitrogen or oxygen atoms. This graftable monomer is then grafted onto a polyolefin backbone having a weight average molecular weight of from about 10,000 to about 750,000 to form a graft copolymer that has dispersant viscosity index improving properties. More particularly, the aforesaid polyolefin backbone is dissolved in a solvent, and the graftable monomer and an initiator are added to the resulting solution. In the alternative, a melt-blending procedure can be employed to graft the graftable monomer onto the aforesaid polyolefin. The aforesaid Goldblatt et al., '713 also discloses a lubricating oil composition comprising a hydrocarbon base oil and the aforesaid graft copolymer.
Goldblatt et al., U.S. patent application Ser. No. 11/912,847, published on Nov. 27, 2008 as Publication No. 2008/0293600A1, discloses a multifunctional grafted polymer containing two groups of monomers grafted to a polyolefin or polyester backbone having a weight average molecular weight from about 10,000 to about 1,000,000, one group of monomers to impart dispersancy, viscosity index improvement and sludge and varnish control as well as another group of monomers to impart soot handling. Generally, one such group of monomers comprises ethylenically unsaturated, aliphatic or aromatic monomers having 2 to about 50 carbon atoms containing oxygen or nitrogen, or both oxygen and nitrogen and imparts dispersancy, viscosity index improvement and sludge and varnish control. Another such group of monomers, the acylating agent provides acyl groups for reaction, and reacts with amines to form substituents that are suitable for imparting soot handling performance. In general, such amines are comprised of primary and secondary amines that can undergo a condensation reaction with an appropriate acylating agent.
Goldblatt et al. '847 also discloses a lubricating oil comprising a hydrocarbon base oil and a multifunctional grafted polymer described above. The multifunctional grafted polyolefin or polyester functions as an additive to control viscosity, sludge, varnish, and soot. Such lubricating oils utilize both (a) the superior dispersancy and (b) the soot control properties of the disclosed multi-functional grafted polymers and thereby require lower amounts of the other additives or fewer additives.
Goldblatt et al. '847 also discloses an effective method of making the aforesaid multi-functional graft polymer in which the grafting sequence is important in order to generate the multi-functional graft polymer described herein. In order to achieve good performance with respect to both soot handling and sludge and varnish control, it is important to first graft a graftable acylating agent onto the polymer backbone to thereby form a polymer containing acyl groups. Next, the monomer or monomer grouping associated with sludge and varnish handling is introduced and reacted. Finally, the amine or amines capable of undergoing a reaction with the acyl group, is introduced and reacted with the acylated polymer thereby imparting soot handling performance to the graft polymer.
To provide improved wear performance, conventional lubricants are formulated with an anti-wear additive. Metal hydrocarbyl dithiophosphates, particularly zinc dialkyldithiophosphates (ZDDP), are the primary anti-wear additives, used in lubricating oils for internal combustion engines. ZDDP provides excellent wear protection at a comparatively low cost and also functions as an antioxidant. However, there is some evidence that phosphorus in lubricants can shorten the effective life of automotive emission catalysts. Accordingly, industry has limited the amount of phosphorus that lubricants can contain. The previous industry category (ILSAC GF-3) mandated a lubricant phosphorus limit of 1000 ppm. The current category of service fill oils in the United States (ILSAC GF-4) mandates even more stringent limits, a maximum phosphorus content of no more than 800 ppm. Future standards may require even more stringent limits, such as a maximum phosphorus content of no more than 500 ppm.
To meet these emerging requirements, it would therefore be advantageous to provide lubricating oils, particularly lubricating oils formulated with base oils having relatively high viscosity indices and low volatilities for improved fuel economy, that also provide excellent low temperature valve train wear performance and anti-oxidant properties with reduced amounts of phosphorus-containing anti-wear additives.
Khorramian, U.S. Pat. Nos. 5,346,635 and 5,439,605 describe lubricating oils completely free of phosphorus-containing anti-wear additives containing a complex blend of ashless friction reducers, ashless anti-wear/extreme pressure additives, antioxidants, metal detergents and polymeric viscosity modifiers and flow improvers, which compositions purportedly provide acceptable properties. These compositions may also contain a molybdenum-containing additive as a friction modifier.
Boden et al., U.S. Pat. No. 5,523,008, which is incorporated herein by reference in its entirety, describes polyolefins containing nitrogen-containing and/or oxygen-containing monomers for use as dispersant viscosity index improvers. The grafted polyolefin contains at least about 13 moles of N-vinylimidazole (similarly known as 1-vinylimidazole), or other ethylenically-unsaturated nitrogen-containing and/or oxygen-containing monomers, per mole of a grafted polyolefin backbone. Also described is a lubricating oil comprising a lubricant base oil and a grafted polyolefin as described above as well as a method of making a dispersant-viscosity index improver. N-vinylimidazole or other ethylenically unsaturated nitrogen-containing and/or oxygen-containing monomers and a graftable polyolefin are reacted with sufficient initiator to graft at least about 13 moles of the monomer to each mole of the polyolefin.
Sauer, U.S. patent application Ser. No. 11/371,481 published on Sep. 14, 2006 as Publication No. 2006/0205611A1, discloses a multiple function polymer comprising a graft polymer of a polyolefin having a weight average molecular weight of from about 20,000, to about 500,000, a nitrogenous, ethylenically unsaturated, aliphatic or aromatic monomer having from 2 to about 50 carbon atoms, which imparts dispersancy which is associated with sludge and varnish handling, and an organo-metallic compound which is capable of reacting with said polyolefin and which imparts anti-wear properties. The organo-metallic compounds comprise metal carboxylates and metal oxides, and further comprise a metallic member selected from the group consisting of molybdenum, cobalt, titanium, calcium, magnesium, manganese, bismuth, tungsten, and copper. The multiple function grafter polymer contains from about 8 to about 16 moles of the nitrogenous ethylenically unsaturated monomer and about 2 to 5 moles of the organometallic monomer.
Sauer '481 also discloses a process for making the aforesaid multiple function graft polymer. The disclosed process comprises the steps of providing a polyolefin having a weight average molecular weight of from about 20,000 to about 500,000, an initiator, and an aforesaid nitrogenous, ethylenically unsaturated, aliphatic or aromatic monomer having from 2 to about 50 carbon atoms that is capable reacting with the aforesaid polyolefin. The polyolefin is dissolved in a solvent forming a solution, and the nitrogenous ethylenically unsaturated monomer is dispersed in the resulting solution. The initiator is added to the solution at a temperature exceeding the initiation temperature of the initiator so that a dispersant polymer is formed. The resulting solution is maintained at the same temperature, and an aforesaid organo-metallic compound is added to the resulting solution and at the same temperature and is grafted to the graft dispersant polymer, thereby forming the aforesaid multiple function polymer.
Sauer '481 also discloses a lubricating oil composition comprising a lubricant base oil, at least about 0.1 percent by weight of the aforesaid multiple function polymer, and from 0 percent to about 4 percent by weight of other dispersants. Such lubricating oil employs both the superior dispersancy and anti-wear properties of the multiple function grafted polymer, thereby requiring fewer additives.
The inventors of the present invention have now discovered a novel multiple function graft polymer for lubricating oil compositions. The multiple function graft polymer imparts dispersancy and control of viscosity, sludge, varnish and soot, and additionally has anti-wear and anti-friction properties, without having an adverse effect on anti-oxidant properties.